Asphalt Materials for Airfield Pavements

Transcription

1 Asphalt Materials for Airfield Pavements John Duval, P.E. Pavement Services, Inc. CAPTG Workshop September 15, 2014 Vancouver, British Columbia

2 Overview Introduction Asphalt Binder Material Considerations for FAA Item P-401 G Future?

3 FAA P-401 G Asphalt cement binder. Asphalt cement binder shall conform to ASTM D6373 Performance Grade (PG) [ ]. A certificate of compliance from the manufacturer shall be included with the mix design submittal. The supplier s certified test report with test data indicating grade certification for the asphalt binder shall be provided to the Engineer for each load at the time of delivery to the mix plant.

4 Binder Selection for Airfield Pavements

5 PG Selection General Concepts Correct binder grade needs to be specified to obtain optimum mixture performance Determine grades that are available and typically being used for particular area from local authorities and/ or AI binder spec database ( In theory, PG system is blind to modification (modified or not, and type of modification) Some states use straight PG system Other states use PG-Plus tests to ensure type and amount of modification

6 P-401 G - PG Guidance P-401 G references AI MS-26 The Asphalt Binder Handbook. Base grade determined as grade used by state DOT for the specific project location, for Interstate Highways (no grade bump). Grade bump (high temp side only) from base grade per Table A for top 5 inches of pavement.

7 Grade Bumping Guidance P-401 G, Table A Aircraft Gross Wt. (pounds) High Temperature Adjustment to Base Binder Grade All Pavement Types 12,500 lbs --- < 100,000 lbs 1 Grade 100,000 lbs 2 Grades

8 P 401 / P-403 Table A - NOTES PG grades above a 22 on the low end (e.g., PG XX 16 or PG XX-10) are not recommended. Limited experience has shown an increase in block cracking with -16 or -10 grade asphalts. Typically, when the PG spread between the high and low temperature is 92 or more, the asphalt cement binder has been modified. A PG Plus Test will be required to determine if the asphalt cement binder has been properly modified. Use the PG Plus Test found in the Asphalt Institute s State Binder Specification Database for the project location. When a State does not specify a PG Plus Test, use ASTM D6084 with a minimum elastic recovery of 70%.

9 Example Select PG grade for taxiway project at Denver Airport, Colorado (> 100,000 lb aircraft) using AI State Binder Spec Database and state highway dept reference, using P-401 G guidance

10 AI Binder Spec Database Summary document for each of 50 States: Standard template PG testing requirements on page 1 PG-Plus test requirements on page 2 Lists Typical grades used Test methods and criteria Any exclusions, required modification methods, etc Agency contact Website for actual spec Kept current and available at:

11 Screenshot AI Public Homepage Binder Specs Emulsion Specs

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13 Colorado DOT Binder Spec Summary Sheet

14 Colorado DOT Binder Spec Summary Sheet Checking with CDOT, PG is standard base grade for the Denver area.

15 Now Grade Bump per Table A in P-401 Aircraft Gross Wt. (pounds) (pounds) High Temperature Adjustment to Base Binder Grade All Pavement Types 12,500 lbs --- < 100,000 lbs 1 Grade 100,000 lbs 2 Grades Bump from to 76-22

16 Similar Example Select PG grade for same project, but now use LTPPBind software 98% reliability) to determine base binder grade

17 LTPPBind 98% Reliability, High Temp

18 LTPPBind 98% Reliability, Low Temp

19 LTPPBind Denver Airport Weather Station

20 LTTPBind Denver Airport For 50% reliability (not conservative: binder contributes to failure every other year at both high and low ends), the true grade necessary is PG (but must be in 6 increments). The standard grade of PG gets high temp reliability to 97% and low temp reliability to 95%. If engineer wants above 98% reliability on both ends (typical), then need PG

21 Now Grade Bump per Table A in P-401 Aircraft Gross Wt. (pounds) (pounds) High Temperature Adjustment to Base Binder Grade All Pavement Types 12,500 lbs --- < 100,000 lbs 1 Grade 100,000 lbs 2 Grades Bump from to 76-28

22 Summary Binder Selection Selecting the correct PG binder is critical to ensure pavement performance Guidance in P-401 G Determine base grade, then bump high temp side per Table A to address tougher loading conditions Two methods for determining base grade Consult with Local DOT LTPPBind software Make sure binder grade is available locally

23 Modified Binders Unmodified (neat) binders often adequate for low to moderate climates and light loading situations Modified binders often needed for more severe climates and/or heavier loading conditions More expensive but improved performance Various types of modification types, including polymers (elastomers and plastomers) and chemicals

24 Guidance on Modified Binders Typically, when the PG spread between the high and low temperature is 92 or more, the asphalt cement binder has been modified. A PG Plus Test will be required to determine if the asphalt cement binder has been properly modified. Use the PG Plus Test found in the Asphalt Institute s State Binder Specification Database for the project location. When a State does not specify a PG Plus Test, use ASTM D6084 with a minimum elastic recovery of 70%.

25 Polymer Modified Asphalt (PMA) The purpose of a PG Plus test is to ensure the presence of elastic modifiers and a minimum level of elastomeric behavior Typical PG Plus tests: Elastic Recovery ASTM 6084 Phase Angle Ductility / Toughness and Tenacity

26 State DOTs Specifying PG-Plus to Ensure Presence of Polymer Ductility ER ER Ductility, TT & ER TT & DT ER & TT ER ER PA ER & FD ER & TT ER & PA ER ER ER FD ER SB/SBS Required ER ER SB/SBS Required FD & ER ER ER & PA PA PA ER-Elastic Recovery FD-Force Ductility TT-Toughness & Tenacity PA-Phase Angle PG-Plus PG

27 Elastic Recovery Test Method 1 2 Neat doesn t recover 3 4 Modified recovers

28 Material Considerations in P-401 G Item P-401 Plant Mix Bituminous Pavement Item P-403 Hot-Mix Asphalt (HMA) Pavements (Base, Leveling or Surface Course) In both specifications, the use of the Gyratory Compactor for design of HMA is a tailoring option that is available to all engineers on all projects. The AC contains no limitations to the use of Gyratory mixes on airport projects.

29 Material Considerations in P-401 G ********** This specification contains options for both Marshall and Gyratory Mix Design Methods. The Engineer shall select the options for the selected mix design method. **********

30 Choose Mix Design Method Marshall Gyratory Reference: AC 150/ G

31 Marshall Criteria, P-401 Table 1 Test Property No. of Blows Stability, lbs (min) Flow, 0.01 in Target Air Voids, % Gross Wt 60 kips or Tire Pressures 100 psi Reference: AC 150/ G Gross Wt < 60 kips or Tire Pressures < 100 psi

32 Mixture Criteria, P-401 Table 2 Maximum Particle Size Minimum VMA Gradation 3 16 % Gradation 2 15 % Gradation 1 14 % Reference: AC 150/ G

33 P-401(G) Gradation Bands Reference: AC 150/ G

34 Gyratory Criteria, P-401 Table 1 Test Property No. of Gyrations Target Air Voids, % Gross Wt 60 kips or Tire Pressures 100 psi Gross Wt < 60 kips or Tire Pressures < 100 psi Reference: AC 150/ G

35 Mixture Criteria, P-401 Table 2 Maximum Particle Size Minimum VMA Gradation 3 16 % Gradation 2 15 % Gradation 1 14 % Reference: AC 150/ G

36 Stability Stability (lb) Flow Flow, 0.01 in Air Voids, % VMA VMA, % VFA VFA, % Interpretation of GyratoryTest Data Plot averages vs. asphalt content % % V a Asphalt Content (%) Asphalt Content (%) 60% 40% 20% 0% Asphalt Content (%) Asphalt Content (%) Asphalt Content (%)

37 ASTM D 4867 Moisture Sensitivity 6 specimens compacted to 6-8% air voids o 3 conditioned and 3 unconditioned Conditioned specimens o 55 to 80 percent saturation o Freeze-thaw cycle o 24 hour soak in 60 C water bath o Cooled to 25 C and broken on IDT Tester Unconditioned specimens o Left undisturbed until broken on IDT Tester TSR 75% If less, try adding LAS, hydrated lime or changing aggregate/binder combination

38 Reclaimed Asphalt Pavement ********** Engineer will determine if RAP is/is not allowed and make appropriate selection. RAP should not be used for surface mixes, except on shoulders. It can be used very effectively in lower layers or for shoulders. Engineer to specify the maximum percentage of reclaimed asphalt allowed in the mix. The amount of RAP shall be limited to 30%, as long as the resulting recycled mix meets all requirements that are specified for virgin mixtures. The Contractor may obtain the RAP from the job site or an existing source. ********** Reference: AC 150/ G

39 Toward a Unified Airfield 2014 Specification AC G 20XX? Unified Airfield Construction Specification For Civil and Military Applications UFGS

40 Asphalt Materials for Airfield Pavements Thank You! Photo Courtesy Steve Muench John Duval, P.E.